Polyaxial screw assembly

ABSTRACT

A polyaxial screw assembly includes an internal load dampening mechanism for sharing and dampening loads between at least one screw member and at least one rod member interconnected by the assembly. A method of interconnecting the orthopedic screw with the rod includes dampening with a body member interconnecting the screw to the rod.

CROSS-REFERENCE TO RELATED APPLICATIONS CROSS-RELATED REFERENCE SECTION

This application is a continuation application of U.S. patentapplication Ser. No. 12/756,212, filed Apr. 8, 2010, which is aContinuation of U.S. patent application Ser. No. 12/343,551, filed Dec.24, 2008, which claims the benefit of priority under 35 U.S.C. Section119(a-d) of U.S. Provisional Patent Application Ser. No. 61/095,485,filed Sep. 9, 2008, all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to orthopedic devices and, morespecifically, to spinal stabilization systems which can particularly beused in the therapeutic correction of scoliosis.

BACKGROUND OF THE INVENTION

The present invention generally relates to polyaxial screw technologyand, more specifically, load sharing and its application in polyaxialscrew technology for the spine. In a preferred embodiment, thetechnology can be applied to the treatment and correction of scoliosis.

More specifically, polyaxial screw technology has been in existence fora number of years. While the technology has advanced, the focus of keyadvances have been on providing smaller and stronger means for fixing ascrew that fixes a body member and rod assembly to vertebrae, with eachscrew assembly having the basic structure of a body with pivot meansaround the screw head and a rod slot. If the rod to be disposed in therod slot is not centered relative to the screw head, the body can pivotover to adjust for the misalignment. Examples of such systems areabundant in the art.

Once the polyaxial screw is connected to the rod, the assembly is lockedsuch that the screw angulation is fixed relative to the body portion.For example, U.S. Pat. No. 6,740,086 to Richelsoph, issued May 25, 2004,shows one such system.

In a more uncommon approach, U.S. Pat. No. 4,805,602 to Puno, et al.,issued Feb. 21, 1989 discloses micromotion between a round screw headand a seat of a body member such that the screw is allowed to rotate inthe seat. More specifically, the assembly includes a rod and pluralityof vertebral anchors that are positioned on the spine on either side ofthe spinous process spanning the portion of the spine to be immobilized.The rod is secured to the vertebral laminae by the vertebral anchors.The anchor includes a transpedicular screw member which is secured to avertebrae. A rod support or body member includes a cup which capturesthe screw and optionally permits micromotion between the rod support andthe screw. This type of approach leads to other issues, as the surgicalcorrection to the spine cannot be effectively controlled and issues ofthe head rotating in the socket producing failure of the system.Therefore, this type of approach is not common. Of course, the lockingstrength of the spherical head of the screw in the body portion variesfrom design to design, as well as the locking mechanism.

A more specific issue related to polyaxial screw technology is theapplication of load sharing, which has various advantages, includingreduction of adjacent segment degeneration and improved fusion quality.The term “load sharing” in spine relates to the ability of a spinalstabilization device to share loads otherwise placed solely upon thespine or soley on the implants. Conventional methods of spinal fixationutilize a relatively rigid spinal fixation device to support an injuredspinal segment or segments being surgically corrected. Such fixationlimits movement of the injured segment. These conventional spinalfixation devices connect and couple rods or plates to fixing screws suchthat the injured spinal segment is supported and held in a relativelyrigid and fixed position by the rods or plates. The connection units,such as the rods and plates, are usually used during fusion, wherebybone graft is inserted into the space and the implants act as internalbraces to stabilize the spine during the bone healing and fusionprocess. The connection units also reduce pain and further injury to thepatient by substantially restraining the movement of the spinal column.However, because the connection interferes with normal movement of thespinal column, negative effects, such as degradation of other healthysegments or pseudoarthrosis can occur causing further complications andissues associated with the spinal column. More specifically, and in thecase of large diameter rods, high rigidity of the rods and/or platesused in conventional fixation devices, the patients fixed joints are notallowed to move after the surgical operation. Consequently, such spinalfixation devices cause decreased mobility of the patient and increasedstress on the remainder of the spinal column joints adjacent to theoperated area. Such excessively rigid spinal fixation can result in whatis termed “stress shielding,” whereby the bone graft used for fusiondoes not receive sufficient loading to allow for solid fusion. Byaltering this approach and allowing load sharing in the spine, we nowhave a reduction of adjacent segment degeneration and improved fusionquality.

An early approach for load sharing was a basic system change from alarger diameter rod to a smaller diameter rod. Newer techniques use moreflexible rods or complex mechanisms placed as connectors between rodsegments.

For example, U.S. Pat. No. 6,241,730 to Alby, issued Jun. 5, 2001, usesa complex link with moveable parts. More specifically, the Alby patentloses an intervertebral link device including at least one damperelement constituted by a cage and a pin designed to be connected to boneanchor elements. The pin is engaged in a housing of the cage and isfitted with two elastically deformable members operating in oppositionto an applied traction force or compression force. The damper element isa pin that is mounted inside the cage by a joint allowingmulti-directional relative pivoting between the pin and the cage, atleast about the axis contained in a plane perpendicular to the pin andangular abutment between the cage and the pin enables themulti-directional relative pivoting to be limited in amplitude to apredetermined value of about 4°.

U.S. Pat. No. 7,326,210 to Jahng, et al., issued Feb. 5, 2008, uses aflexible rod constructed from two different materials. Morespecifically, the flexible connection unit used for use in a spinalfixation device includes a longitudinal member having first and secondends and at least one spacer located between the first neck and secondends wherein the spacer includes a first portion made from a firstmaterial and a second portion made from a second material and at leastone flexible member located in a longitudinal axial channel of thespacer wherein the first and second ends substantially limit motion ofthe spacer in the longitudinal axial direction with respect to theflexible member.

Both of the above techniques have drawbacks due to the complexity, size,strength, or inability to integrate into effective spinal stabilizationsystems. Their use is substantially directed to fusion techniques.Stabilization of the spine for non-fusion is a totally different matterraising totally different issues. Flexion of the spine creates very highloads on the screw-bone interface and often causes loosening of thescrews from the vertebrae. Common complications are for the screw to bepulled loose or screw failure, thereby totally destabilizing thefixation device.

The present invention provides a much simpler device from an engineeringpoint of view yet effective in both fixation during fusion andnon-fusion techniques. This allows for many options in the treatment ofthe spine with the same basic system. In addition, the present inventioncan be utilized for stabilization and reduction during the treatment ofscoliosis.

Scoliosis is the medical term for curvature of the spine. Scoliosisoccurs in approximately 2% of women and less than ½% of men. It usuallystarts in the early adolescence and may gradually progress as rapidgrowth occurs. However, scoliosis can occur at any age from juvenile toadult. Persons with a curve of 10° or less are often thought to havejust an asymmetry of the spine, but in children who end up withsignificant curves, a 10° curve can progress to a 50° curve and asignificant deformity if there is enough growing time remaining. Personswith curves measuring under 30° entering adulthood are considered havinga mild curve while those over 60° are considered severe. Treatment isrecommended, depending on the severity and the age of the person. Itwould be advantageous to be able to correct the severity before itprogresses while the spine is still growing, and various techniquesalong with various devices, such as the one covered by U.S. Pat. No.6,554,831 by Rivard et al. have been developed, but these devices andtechniques are not well developed and have complications. Adapting arigid prior art system to the treatment of early onset scoliosis wouldresult in degenerative growth of the spine due to the fixed nature ofprior art systems or repetitive surgeries.

There are generally three options to the treatment of scoliosis. Thefirst option is doing nothing. This may be a reasonable decisiondepending on the age of the patient and the predicted outcome. If theperson is a teen or pre-teen and the prediction is that this curve willworsen, then doing nothing may not be appropriate. As the curveprogresses, torso deformities occur. In the more severe curves, internalorgans are compressed. Without surgery, such patients risk organ damageor failure. On the other hand, if the person has reached maturity, thenif the curve is mild, below 40°, it may not increase any more. A secondoption is to wear a brace. Bracing has been shown to be a somewhateffective method of controlling the curve progression, but it does notcure scoliosis. From a practical aspect though, this treatment isreserved for children and adolescents in whom the prediction of a rapidincrease in the curve needs to be thwarted. However, a brace worn even23 hours per day and worn properly does not guarantee that the curvewill not continue to increase.

The third option of treatment is surgery. For those persons who alreadyhave a significant curve with a significant deformity, surgery canreduce the curve and significantly reduce the deformity.

The usual scoliosis curve is a thoracic curve. In these curves, thegeneral procedure is a posterior spinal fusion. The fusion is aprocedure wherein the individual vertebra are fused to the one above andbelow. Typically, ten or more segments are included. Scoliosis alsoaffects the lumbar spine as well, often requiring very long fusions ofthe spine.

It should also be noted that scoliosis a three-dimensional problem, withthe curvature of the spine occurring not only in the coronal plane, butusually in angles relative to the coronal plane. One of the aims ofsurgery is to try to restore the normal contour of the back from boththe front view and the side view to restore normal function, balance,and cosmetics.

The spine has normal curves when looking from the side but it shouldappear straight when looking from the front. Kyphosis is generally acurvature of the upper spine, which when seen from the side the spine isbent forward. Lordosis is a curve that has its convexity anteriorly andconcavity posteriorly. People with scoliosis develop additional curvesto either side and the vetebrae of the spine twist on each other like acorkscrew.

The present invention addresses various issues encountered in the priorart. Generally, angulation of a polyaxial screw is a means ofcompensating for a rod that is offset relative to a screw that isinserted into the pedicle, as used above. However, angulation is not thekey issue. Rather, the offset is the key issue. With regard to the issueof the rigidity of prior art systems, the present invention allows forlocking of a polyaxial screw rigidly at a desired angulation but thepresent invention also provides load sharing. Hence, the two aspects ofthe design are not mutually exclusive as in the prior art. Accordingly,combining angulation of the polyaxial screw with additional offsetcapability allows an increase in the amount of angulation over the priorart. Likewise, combining load sharing of external components into aninternal mechanism within the polyaxial screw while still utilizingstandard rods eliminates complex external mechanisms or materialssubject to failure. Thus, the present invention provides a polyaxialscrew that can moderate loads relative to the direction of the loadexerted by the force on the rod from adjacent levels.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a polyaxialscrew assembly including internal load dampening means for sharing anddampening loads between at least one screw member and at least one rodmember interconnected by the assembly.

The present invention further provides a method of interconnecting anorthopedic screw with a rod by load dampening with a body memberinterconnecting the screw to the rod.

DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention are readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawingswherein:

FIG. 1 is a elevational view of a polyaxial screw assembly made inaccordance with the present invention;

FIG. 2 is a perspective view of the polyaxial screw assembly;

FIG. 3 is an exploded view of the polyaxial screw assembly;

FIG. 4 is a line drawing of an exploded view of the polyaxial screwassembly;

FIG. 5 is a perspective view of a body member made in accordance withthe present invention;

FIG. 6 is a cross-sectional view in perspective of the body member;

FIG. 7 is a cross-sectional view of a locking ring member;

FIG. 8 is an elevational view of a screw member made in accordance withthe present invention;

FIG. 9 is an elevational view partially exploded of the screw member andlocking assembly of the present invention;

FIG. 10 is an elevational view, partially in cross-section, of the screwmember and locking assembly in the locked position;

FIG. 11 is an elevational view, partially in cross-section, of the screwmember and locking assembly in the locked position inside the bodymember;

FIG. 12 is an elevational view of the screw member within the lockingassembly in a locked position inside the body member;

FIG. 13 is an elevational view in perspective, partially broken away ofthe screw member and locking assembly in the locked position inside thebody member also including the load sharing damper of the presentinvention;

FIG. 14 is an elevational view in perspective, partially broken away ofthe locking assembly in the locked position inside the body memberincluding the load sharing damper;

FIG. 15 is a perspective view showing the assembly, with the body memberpartially broken away;

FIG. 16 is an elevational view, partially broken away of the inventionshowing the screw member relative to the body member locked and angled;

FIG. 17 is a perspective view, partially broken away, of the presentinvention wherein the screw member is aligned with the longitudinal axisof the body member;

FIG. 18 is an elevational view, partially broken away and in perspectiveof the present invention wherein the screw member is angled relative tothe longitudinal axis of the body member;

FIG. 19 is a top perspective view of the rod locking member of thepresent invention;

FIG. 20 is a bottom perspective view of the locking member;

FIG. 21 is a partially exploded view of the present invention with therod member not locked within the present invention;

FIG. 22 is an assembled perspective view of the present invention withthe rod member locked therein;

FIG. 23 is a top perspective view of the body member of the presentinvention;

FIG. 24 is a top perspective view of the body member of the presentinvention including the locking ring for locking a rod therein;

FIG. 25 is a side perspective view of the assembly shown in FIG. 24;

FIG. 26 is an alternative embodiment of the present invention;

FIG. 27 is a top side perspective view of the present invention;

FIG. 28 is a perspective view showing the screw head top portion;

FIG. 29 is an elevational view of a further embodiment of the bodymember of the present invention retaining a screw member therein;

FIG. 30 is a perspective view of a further embodiment of the presentinvention;

FIG. 31 is an elevational view of the embodiment shown in FIG. 30;

FIG. 32 is a perspective view of the embodiment shown in FIGS. 30 and 31including a rod retained therein;

FIG. 33 is a perspective view of a further embodiment of the presentinvention;

FIG. 34 is a perspective view of a rod retaining bearing made inaccordance with the present invention;

FIG. 35 is a perspective view of a rod bearing retaining assembly madein accordance with the present invention;

FIG. 36 is a perspective view of the body member retaining a screwincluding means for retaining the rod bearing retaining assembly;

FIG. 37 is a cross-sectional view of the rod bearing;

FIG. 38 is a side view partially in cross section of a rod bearingretaining a rod member therein;

FIG. 40 is an elevational perspective view of the present inventionretaining a curved rod therein;

FIG. 41 is a perspective view of the present invention including a rodretained therein rotated 90° from the position shown in FIG. 40;

FIG. 42 shows a perspective view of the present invention indicatingrotation of the rod member within the assembly 90°;

FIG. 43 is a side perspective view of a further embodiment of thepresent invention retaining a curved rod therein;

FIG. 44 is a perspective view of the assembly made in accordance of thepresent invention retaining two rod members therein;

FIG. 45 is a perspective view of the present invention also showing tworod members retained therein;

FIG. 46 is a side elevational view of the present invention showing arod retained between two body members;

FIG. 47 a is a perspective view of a dual rod retaining body member;

FIG. 47 b is a line drawing of the assembly shown in FIG. 47 a;

FIG. 48 a is a top perspective view of a dual rod retaining assemblymade in accordance with the present invention;

FIG. 48 b is a line drawing of the assembly shown in FIG. 48 a;

FIG. 49 a is a top perspective view of a dual rod retaining assemblymade in accordance with the present invention;

FIG. 49 b is a line drawing of the assembly shown in FIG. 49 a;

FIG. 50 is a further embodiment of a dual rod retaining body memberassembly;

FIG. 51 is another embodiment of the rod retaining body member includingbearing members rotated therein;

FIG. 52 a is a top perspective view exploded of the present invention;

FIG. 52 b is a line drawing of the assembly shown in FIG. 52 a;

FIG. 53 is a side perspective view exploded of the present invention;

FIG. 54 a is a side elevational view in perspective of a furtherembodiment of the present invention;

FIG. 54 b is a line drawing of the assembly shown in FIG. 54 a;

FIGS. 55 a and b are plan views of a multi-segment system of the presentinvention in an initial position (left) and with the rods rotated 90°(right);

FIG. 56 is a side plan view line drawing of a slidable housing andcollet on a rod;

FIG. 57 is a plan view of the assembly shown in FIG. 56;

FIG. 58 is a perspective view of an alternative embodiment of thepresent invention; and

FIG. 59 is a cross-sectional view of the embodiment shown in FIG. 58.

DETAILED DESCRIPTION OF THE INVENTION

A polyaxial screw assembly made in accordance with the present inventionis generally shown at 10 in the Figures. Primed numbers indicate likestructure amongst the several embodiments. Each of the assemblies 10shown can include an internal load dampening mechanism for sharing anddampening loads between at least one screw member and at least one rodmember interconnected by the assembly 10. The term “load dampeningmechanism” means that the assembly within a body member thereofdescribed below, includes an absorptive mechanism for dampening loadstransmitted between the articulating vertebrae, through the screwmember, into the body member, along a rod, and passing to another bodymember. As explained below in greater detail, this allows forarticulation of vertebrae interconnected by the present invention whileloads transmitted through the system are dampened. This internal loaddampening is accomplished through a compact efficient assembly and iseffective to prevent deleterious stresses placed on the system, andespecially the screw members. It also allows, in a fusion, for dampeningof otherwise unnatural stresses imposed on the non-fused segments by therigidity of the fused sections. This internal dampening ability, incombination with the ability of the present invention to articulate in anovel manner and, the body members to allow sliding along interconnectedrod members results in a sophisticated system for allowing growth of thesystem concomitant with vertebrae growth. The present invention is wellsuited for the treatment of spinal deformities, such as scoliosis. Theability of the system to grow with the growth of the vertebrae makes thepresent invention particularly well suited for the treatment ofprepubescent patients whose spines will grow yet require early onsettherapeutic manipulation by the system.

Referring more specifically to the drawings, and in particular at FIGS.1-4, the polyaxial screw assembly 10 includes a body member generallyshown at 12 for interconnecting a screw member generally shown at 14 toa rod member generally shown at 16. The body portion 12 interconnectsthe screw member 14 which is fixedly secured to a vertebra to a rodmember 16. The rod member 16 is used to interconnect the body member 12with another body member 12 which would itself be fixedly secured toanother vertebra via another screw 14. Examples of such interconnectionsare shown in FIGS. 46 and 55 a and 55 b. Such assemblies can beconstructed with other devices known in the art, such as plates,fusions, etc.

Generally referring to the components of the assembly 10, the screwmember 14 includes a threaded body portion 18 and a head portion 20. Asbest shown in FIGS. 3 and 4, the head portion 20 can befrusto-spherical, having a flat end portion generally including ahexagonal recess for insertion purposes by an appropriate hex tool.

The body member 12, as best shown in FIG. 6, includes an opening 22extending therethrough defining a longitudinal axis indicated in FIG. 6at 24.

The body member 12 can be divided into two subportions, a firstsubportion for retaining the head 20 of the screw 14 therein and asecond portion for retaining the rod member 16 therein. The firstportion for retaining the head portion 20 of the screw member 14 thereinincludes a recessed portion or surface 26 between a first lip 28 andsecond lip 30 which extend both radially inwardly into the opening 22. Athird radially inwardly extending lip 32 defines a pocket 34therebetween. The function of these recesses or pockets will beexplained below.

The rod retaining portion of the body member 12 includes a pair of arms36, 38, as best shown in FIG. 5. Between each of the arms 36, 38 isdefined a U-shaped pocket or seat 40 such that a rod member 16 can bedisposed within the pocket 40. The inner wall 42 of each arm 36, 38includes a groove 44 for retaining a locking member therein as describedin greater detail below.\

The head 20 of the screw member 14 can be locked within the lowerportion of the body member 12 by various means well known in the art.For purposes of illustration, the present invention includes a lockingmechanism, the components of which are shown in exploded view in FIGS. 3and 4. Specifically, locking collar 48 is retained within recess 26 ofthe body member 12 and prevented from escape by lip 28. Collar 50 isdisposed within collar 48 and retained therein as the screw threadedportion 16 is disposed through each of the collars 48 and 50 and thescrew head 20 is seated against collar 50. Screw locking member 52 isdisposed within opening 26 and retained therein by lip portion 30thereby locking the screw head 20 in a substantially fixed position. Theangle of the threaded portion 16 of the screw member 14 relative to theaxis 24 of the body member 12 can be adjusted prior to locking of thescrew head 20 thereby creating desired angulation, in its simplest form.Greater adjustment will be discussed below.

FIG. 7 shows an enlarged cross-sectional view of the locking ring 48having an internal surface which is tapered at 54. As compression isapplied against the screw head 20 between the locking member 52 andseating ring 50, the seating ring is driven into the locking ring 48against the taper or curvate surface 54 to compress against and lock inposition the screw head 20. Another preferred variation is that theinternal surface of locking ring 48 has an engagement portion that issmaller than the screw head 20. Compressing the screw head 20 downwardinto this smaller diameter area creates force on the screw head 20,thereby locking the angle of the screw. Again, other variations oflocking mechanisms can be utilized in accordance with the presentinvention. FIGS. 9-12 illustrate the screw head 20 and the variouscomponents used above locking the screw member 14 relative to the bodymember 12. It is also possible to adjust the locking ring 48 and screwhead 20 such that the screw can be locked at specific loads and whenthose loads are exceeded, the screw head 20 moves in the locking ring48.

As discussed above, the arms 36, 38 form a U-shaped recess or pocket 40for receiving a rod member 16 therein, as shown in various views, forexample, FIGS. 1, 2, and 22. The rod member 16 is fixedly retained inthe pocket 40 by means of a locking member, generally shown at 58 invarious figures. FIGS. 19 and 20 show the locking member in a top andbottom perspective view, respectively, the locking member 58 being asubstantially U-shaped member when viewed in elevation, including legportions 60 and 62 and base portion 64 combining to form a substantiallyU-shaped pocket 66. A radially outwardly extending rib 68 projects froman annular peripheral surface of the base portion 64.

FIG. 22 shows an exploded view of the screw member 14 secured within thebody portion 12, the details of which will be described below. The rodmember 16 is disposed above the portion of the body member 12 that willreceive the rod member 16, the locking member 58 being separate from theassembly. FIG. 22 shows the rod member 16 captured within thesubstantially U-shaped pocket 40 of the body member 12 with the lockingmember 58 capturing the rod member 16 between the substantially U-shapedpocket 66. The pockets 40 and 46 engage the rod member 16 to fixedlysecure it in place as the rib 68 of the locking member 58 is engaged andsecured within recess 70 formed in each of the arms 36, 38 of the bodymember 12.

The structure of the body member 12 relative to the locking member 58can be modified, such as the body member 12 including an inwardlyradially projecting rib, which would mate with a recess formed in thelocking member 58. Likewise, other locking member configurations can becontemplated and executed in accordance with the present invention. Forexample, FIG. 29 shows arms 36′, 38′ including a threaded inner surface74. As shown in FIGS. 30-32, the locking member 58′ includes a threadedouter surface for threadingly engaging the threaded inner surface of thearms 36′, 38′ and thereby locking down upon the rod member 16 disposedtherein. Again, there are other locking mechanisms either known in theart or not yet contemplated that can be used in accordance with thepresent invention in order to fixedly secure the rod member 16 withinthe body portion 12 thereby interconnecting the rod member 16 to thevertebrae in which the screw member 14 is implanted.

For example, FIGS. 23-27 show an alternative locking mechanism, which isa collet type locking device that eliminates the requirement of aretaining ring within the assembly. Such a system is shown in U.S.patent to Richelsoph et al., issued Mar. 12, 2002, which uses a bodymember 12 including a pair of flexible arms 80, 82 defining a U-shapedflexible seat 84. The flexible arms 80, 82 allow for free slidableadjustment of a rod 16 disposed within the seat. The rod is in anuncompressed condition when the rod is seated within the seat therebyallowing for movement of the rod within the seat. The arms 80, 82 have asmooth outer surface 86, 88 and an outwardly flared end portion 90, 92which is compressed in a rod receiving member 96 for locking the rod 16in position relative to the body member 12. Again, the construction canbe reversed such that the collet is smooth on the arms without anoutward flare and the body member includes a ridge, such that the armsare pushed further against the rod as the collet is pushed into thebody. In other words, various aspects of the general structure describedabove can be modified within the contemplation of the present invention.

A significant aspect of the present invention is internal load dampeningmeans which share and dampen loads between at least one screw member 14and at least one rod member 16 interconnected by said assembly 10. Morespecifically, the body member 16 includes the screw seat 26, which seatsa screw head 20 therein. The load dampening mechanism includes at leasta portion of the screw head seat, the screw head seat being defined asthe walls containing the screw head seated within the body member 12. Inthe specific embodiment shown in the Figures, and presently specificallyreferring to FIGS. 3 and 4, the screw head 20 is disposed between rings48, 50 and locking ring 52 within the recess 26 of the body member 12.Dampening member 98 shown in the exploded views of FIGS. 3 and 4, isfixedly disposed within recess 34 of body member 12. Assembled views areshown in FIGS. 13-18 and 22. The load dampening ring member 98, whenpositioned in abutting engagement against the locking ring 52 provides aload absorbing mechanism against which forces generated by movingvertebrae through screw member 16 can be absorbed within the assembly10. Thus, the recess 34 provides ring retainer means for retaining thering member 98 therein. The ring 98 defines an upper wall against whichthe screw head and screw head locking mechanism abuts thereby allowingthe resilient retainer ring to flex and absorb loads within the assembly10. Of course, the ring 98 absorbs loads traveling both ways through theassembly 10 such that loads placed on rod member 16 through the bodymember 12 are absorbed and dampened as they are transmitted to the screwmember 14. This allows for greater adjustments of rod position duringreduction, while preventing loads from being transmitted wholly to asingle screw or multiple screws. Rather, loads are transmitted throughthe rod member 16 through the various screws interconnected to the rodby the various body members 12 including the load dampening mechanism ofthe present invention.

Alternative configurations of the load dampening mechanism can becontemplated, such as wherein various walls 26 of the body member areflexible thereby also dampening loads transmitted from a rod member 16to a screw member 14 or vice versa. For example, the entire wall of thebody member 12 can form a cup around the head 20 of the screw member 16and locking mechanism thereof to provide load dampening in alldirections about the screw head 20. Alternatively, the entire lockingmechanism can be a load absorbing material so as to be able to dampenloads placed on the screw head 20 or the body member 12 which aretransmitted therebetween. The dampening member would be a liningentirely covering a surface of the screw head 20 within the screw headseat.

The rod member 16 can be made from various materials, such as titaniumalloys, cobalt chrome, and stainless steels. These materials can also becoated for additional strength and/or lubricity.

Consistent with the alternative embodiments used above, the body membercould be made from a load absorbing material or the seat portion of thebody member can be made from a load dampening material, such as metalsand plastics well known in the art. Likewise, the body portion 12 can bemade from a dual durometer material wherein the screw head seat can bemade from a more absorptive load dampening material and the rod retainerportion can be made from a more inflexible material. Such methods ofmaking dual durometer parts are well known in the art.

The screw head 20 seated with the body member 12 but not lockedexperiences a self-centering effect due to the biasing of the loaddampening ring 98. Thus, the present invention further provides aself-centering mechanism for self-centering a screw in the body memberin an unlocked condition.

FIG. 28 shows a further inventive aspect of the present invention.Having a round load sharing/dampening element 98 around a round internallocking mechanism will lock the screw at an angle (an angular lock screwas shown in FIG. 29) but can still rotate in the body 360° along thelong axis 24 (shown in FIG. 6) of the body member 12. The lower face 102(shown in FIG. 6) of the body member 12 and the retaining ring or lowerend of the collet in the embodiments used above, prevent motion that isnot sliding perpendicular to the axis of rotation. In this case, thefriction of the load sharing/damper ring 98 against the inside of thebody member 12 controls the force required for rotation. This rotationis controllable by a variety of means.

In one embodiment, if the external surface of the locking mechanismcomprising rings 48, 50 and 52, shown in FIGS. 3 and 4, are not round,and the load sharing dampening element 98 is not round, then thischanges the ability of the entire combined mechanism to freely rotatewithin the body member 12. For example, as shown in FIG. 28, the outsidesurface of the locking mechanism 52 in combination with rings 48, 50(not shown in FIG. 28) is oval. The larger the oval, the more force isrequired for rotation. If the internal body recess 26 (as shown in FIG.6) is also oval, and the oval of the locking mechanism 52 is largeenough such that one edge of the oval contacts the side of the internalbody wall 26 when rotated, then the amount of rotation can be directlycontrolled to the desired amount. This geometry can be in other shapes,including square or rectangular, or a combination to accomplish the sameeffect. Thus, this geometry provides a screw rotation control mechanismfor controlling the force required to rotate a screw along an axisperpendicularly to an axis defined by the length of the body member 12retaining the screw 14 therein. This is accomplished by the innersurface 26 of the body member 12 and the outer surface of the seatingmechanism comprising the locking rings 48, 50 and 52 having the ovalcross-sectional shape. As stated above, this cross-sectional shape couldbe square, hexagonal, or other shapes.

What is key to greater adaptability of the present invention to variousfinal configurations and needs for reduction is not the rotation of thescrew member 14 relative to the body member 12, but rather the overallmotion parallel to the loads exerted on the rod 16. By allowingcontrolled motion as used above, the loads to the pedicle and spine canbe moderated in multiple directions. This is done with standard spinerods and without the need for PEEK rods, or complex motion mechanisms ofthe prior art. Such an approach has advantages.

For example, it is well understood that a level that is fused alters thespine loads exerted on the levels above and below the fusion. Byallowing the loads at the unaffected levels to be moderated and reduced,the healthy or relatively healthy discs are much better preserved.Hence, problems of the prior art wherein fusion results in eventualdegradation of adjacent discs is minimized or avoided.

In addition, if motion in all planes is required for a perpendicularload sharing and dynamic system, then the load sharing damper mechanismof the present invention can encapsulate the locking mechanism 52, asused above. In this manner, all surfaces of the internal lockingmechanism are suspended away from the internal recess 26 of the bodymember 12. Thus, motion is allowed in all directions, but the amount ofmotion based on the distance or gap between the internal lockingmechanism 48, 50, 52 and the internal body wall 26.

The present invention allows the above-used sliding mechanism to belocked in place by direct pressure or mechanical engagement with the rodlocking mechanism used above. While this does not allow for load sharingand dampening as there is direct locking force from the rod to the screwhead, it does provide a benefit, especially in cervical spineapplications. By allowing the screw 14 to slide, the amount of screwangulation increases (screw angulation being defined as the anglebetween the long axis of the screw member 14 and the axis 24 of the bodymember 12.) For example, as the screw 14 slides to the right, a largergap between the lower edge of the body member 12 and the screw 14 on theleft side occurs. The screw can now rotate further to the left withouthitting the lower edge 102 of the body member 12 as shown in FIG. 29.Thus, the present invention provides a seat mechanism for seating a head20 of a screw 14 therein and includes an outer surface seated within aninner surface of the body member 12 and a mechanism for locking thescrew within the body member such that a gap between the inner and outersurfaces allows motion of the screw 14 relative to the body member 12when the screw is locked within the body member thereby increasingangulation of the screw long axis relative to the axis 24 of the bodymember 12.

In cervical spine manipulations, a high angulation screw is oftenrequired. The load sharing damper of the present invention allows someincreased angulation already by the present approach and it is possibleto adjust this combination of load sharing damping with increased screwangulation according to requirements.

If all of the benefits of the above-described system are considered,then it can be seen that there are benefits to using such a polyaxialscrew assembly 10 with a pediatric scoliosis system. In such a system,the spine elements are generally present and intact, but the curve ofthe spine requires means to straighten it. Fusion of the spine isnormally the treatment of choice as used above in detail, and pediclescrew fixation with rigid rods to hold the spine straight during thefusion process is the preferred treatment. However, it would be farbetter to utilize the present invention that shares the load with thespine, allows for correction, and does not require fusion, but isallowed to grow with the patient. A completely rigid screw, as is commonin the current art, would not be effective in accomplishing this goal.The rods are contoured to match what the spine curve should be and thescrews are rigidly fixed to the pedicles and rods. If a rigid screw wasto slide along the rod, it would have infinite difficulty in movingalong the curves. In addition, the change of the curvature would createextremely high loads on the pedicle, risking not only fracture, butabnormal changes in the desired curvature. This is because as the spinegrows, the screw would be pushed into a different location on the rodthat may have a different curvature. However, utilizing the presentinvention, the load is moderated and the assembly can be moved relativeto the rod to maintain relative alignment without being rigidly fixed tothe rod.

To accomplish the above goal in a scoliosis manipulation or othermanipulation where there would be spinal growth during treatment, theamount of motion is controlled by the gap between the body member 12 andthe internal locking mechanism 48, 50, 52 and the load sharing dampermaterial properties. The more gap, the more potential motion. It istherefore possible to make the body member 12 larger or larger only inone direction, such as oval or rectangular, such that the screw member14 can move greater distances in one direction, such as along the rod.

Secondly, if there is no rod locking mechanism, but a sliding mechanism,the height of the assembly is significantly reduced and the system willliterally grow with the spine. An example of such a mechanism is shownin FIGS. 30, 31, and 32. These Figures show a body member 12′ forinterconnecting the screw member 14 to at least one rod member 16wherein the body member 12′ includes a slidable rod retaining mechanismfor retaining a rod member therein while allowing sliding movement ofthe body member 12 relative to the rod 16. More specifically, the rodmember 16 is retained within a sliding tube 106 disposed over the rodmember 16. The sliding tube can be made from various materials such astitanium, cobalt chrome, stainless, or one of these materials treated orcoated to improve wear properties. Treating the surface with nitrides orcoating in titanium nitride, or diamond like coatings are just a few ofthe possibilities. The sliding tube can also be lined with a plastic,such as polyethylene.

FIG. 33 shows an alternative version 10″ of the present inventionprimarily for the treatment of pediatric scoliosis or, again, otherpediatric manipulations wherein there will be growth of the spine duringtreatment. This version allows for minimally invasive reduction ofscoliosis by allowing for smaller rod segments to be effectivelyconnected by a dual sliding mechanism generally indicated at 110. Thedual sliding mechanism 110 includes two ports 112, 114. Disposed withineach port is a rotatable sleeve 106. The dual port sliding mechanism 110is also constructed so as to rotate 90° relative to the long axis of thescrew member 14 to enable reduction.

By way of background, there are two basic forms of scoliosis reduction.Derotation involves creating the correct curvature for the spine in oneplane and then rotating it 90° such that the curve forces the spine backinto a normal shape. The rod is used as a cam for this purpose. Thesecond method is a cantilever approach, wherein the rod is not rotated,but the rod is formed with the correct curvature and the screw broughtto the rod or vice versa at each level that is secured to the rod. As asystem in the earlier figures can easily accomplish the cantileverapproach, the following approach is a unique method for derotation.

As best shown in FIG. 3, the body portion 12′ includes the retainerportion 110 having internal bearings 106 attached thereto. The bearings106 include an outer wall, as best shown in FIG. 34 at 120 in an innerwall 122. Projecting radially outwardly from the outer surface 120 is alocking tab 124. Two of the bearings 106 slide within the rod retainerportion 112, 114 and are held in place by the tabs 124. The tabs 124 aredepressible such that the bearing members 106 can rotate within the rodretainer portion when the tab 124 is not aligned with and inserted intoopenings 130.

In FIGS. 35 and 36, one embodiment of securing the rod retainer portion110 to the body portion 12′ is shown. The rod retainer portion 110includes a radially outwardly protecting hex portion 132 which can befixedly seated within a groove 134 within an inner surface of the bodyportion 12′. The body member 12′ captures and aligns the head to thebody member 12′. A opening 136 as best shown in FIGS. 40, 41, and 42allows access to locking the screw portion.

FIGS. 37 and 38 show the inside of the bearing 106′ for use with acurved rod. The inside of the bearing 106′ is formed with a curvematching the curve of the preferably pre-bent rod. FIG. 39 shows thebearing 106′ fit with a curved rod 16′.

For scoliosis reduction via derotation, the curved rod 16′ is insertedinto the bearing 106′ such that the curve is aligned on the coronalplane, as shown in FIG. 42. Upon rotating the rod, as shown in FIG. 42by arrow 150, a bearing moves in the rod retainer portion until thecurve is aligned with the sagital plane. When the bearing reaches the90° rotation, the locking tab 124 engages the rod retainer portion andlocks into place. This can be best seen in FIGS. 40, 41, and 42. FIGS.43, 44, and 45 show the rods with the addition of end caps 152 such thatthe rod 16′ cannot slide out of the retainer 110. FIGS. 44 and 45 showthe dual rod construct to connect multiple levels and allow derotationat each level individually.

FIG. 46 shows a stop mechanism for preventing further movement of thebody members 12″ along the rod 16′ beyond the rod stop mechanism. Therod stop mechanism shown is a pair of collets 156 crimped or otherwisefixedly secured to rod 16′ at a predetermined distance apart which abutagainst the body members 12″ to prevent the body members from slidingcloser to each other than the predetermined fixed distance defined bythe collets 156. Such collets or locking collars 156 can be utilized todecompress a nerve. For example, the locking collars 156 can be placedon the rod 16′. These collars 156 can be either slid on the rodbeforehand (closed round rings) or after the rods are placed via a C orU-shaped collet. The collets 156 can be crimped or fastened by othermeans, such as by a set screw. This technique allows for a set distanceto be maintained between the body members 12″, but still allows outwardsliding along the rod 16′. The body members 12″ fixed to vertebrae (notshown) can spread apart from each other as the vertebrae grow. Thepresent locking mechanism for the screw head 20 in combination with thesliding rod retaining members 110 allow for growth of the assembly 10″with the growing spine. Such a system is extremely well suited forpediatric use, especially in the treatment of scoliosis.

An alternative approach to the above is a spacer tube (not shown) whichis effectively a length of tubing that simply slides along the rod 16′.The tube is placed between the screw bodies thus maintaining spacetherebetween. This allows both screws 14 to effectively slide along therod 16′ without any stops, but the distance between the screws is alwaysheld apart at least a minimum amount no matter where the screw or screwsslide.

FIGS. 47-53 show an alternative mechanism for allowing or preventingrotation of the rods 16 within the rod retainer. As shown in FIGS. 47 aand 47 b, the bearing holder 110′ includes at least one locking tab orarm 160 (two are shown in each figure) each having a flexible portionwith internal teeth 162. The locking tab or arm 160 is flexible so as tobe able to bias outwardly to a non-lock position and radially inwardlyto a locking position. Each bearing member 106″, as shown in FIGS. 48 aand 48 b include indentation or teeth 164 machined into the outersurface thereof. Thus, as best shown in FIG. 49 b, the engagement ofteeth 162, with teeth 164 can prevent relative rotation therebetween.Outward flexing of arms 160 releases the teeth 162, 164 from each otherthereby allowing relative rotation in both directions. The teeth can beconfigured, as shown best in FIG. 49 b, to allow rotation in onedirection while blocking rotation in the other unless in the unlocked,outwardly biased condition. Thus, the rod can be rotated in onedirection during reduction yet prevented from derotating or vice versa.FIGS. 50 and 51 show the bearing member 106″ including the toothconfiguration preventing reverse rotation. The teeth configuration 164on the outer surface of the bearing members 106″ also allows for thebearing member 106″ to be inserted within the bearing retainer member110″ and held without any other additional components. Opening 168allows for instrument access to the polyaxial mechanism. This openingalso allows easy observation of the rotation of the bearing members106″.

FIG. 51 shows the relative rotation of the two bearing members 106″, twodots 170 being placed at the normal non-rotated position. The bearing onthe right in FIG. 51 is then rotated. Once rotated, the flats of theteeth 154, 166 engage and will not allow the bearing to rotate back. Forrevision of adjustment, the locking tab or arm 160 can be moved upwardto disengage the teeth to allow rotation.

The use of multiple positions for teeth engagement allows for lockingduring derotation at various points. Thus, if the spinal curve isreduced to an acceptable level at partial rotation of the bearing, it isnot necessary to rotate further. In addition, in a minimally invasiveapproach, it is ideal to do the curve reduction incrementally andwithout the need for locking the rod to the assembly and having tounlock it to make adjustments. The use of multiple position self lockingallows for the implant system to hold position without extra surgicalsteps. In addition, the relative position of the bearing can be relayedby an instrument to the surgeon, such that the surgeon knows by degreesthe amount of derotation that has been done without having to see theimplants under the skin and muscle. This is very important for aminimally invasive approach.

FIGS. 54 a and 54 b show a further version 10′″ of the same conceptdescribed above. The body member 12″″ and bearing holder 172 are asingle unit with rods 16′ and bearings 106″ disposed on the side of thebody member 12″″. The polyaxial angulation is locking in the loadsharing bearing by a locking means, such as a set screw. The rod and rodbearings are now parallel to the body. The rods can also be angled, suchthat the rods are at a 45° angle relative to the body. This reducesheight for an increase in width, or vice versa.

FIGS. 55 a and 55 b show the assembly at multiple connecting points ofthe vertebrae. The left-hand figure shows the rods in the coronal planewhile the right-hand figure shows the rods rotated during spinaladjustment in the sagittal plane. A multi-segmented assembly is shownwhich allows for individual segmental adjustment along the assembly.Hence, segmental adjustments can be individually made during thesurgical process. It should also be noted that excess rod 176 allows forsliding movement and thereby growth of the vertebrae adapting thepresent invention to a pediatric use.

FIGS. 56 and 57 demonstrate the concept of a growing rod whereby a rodin pediatric scoliosis is forced in the direction of the growing spineto assist in curve correction. This general concept has been previouslyused wherein surgeons begin the growing rods program with patients atabout 7 or 8 years old by attaching stainless steel rods to the spine.These rods are fixed to the screws and locked to control the deformityand gradually expanded to straighten the spine while enabling it to growas a result of periodic surgeries in which doctors lengthen the rodsover several years. Although the novel invention disclosed within alongwith a sliding approach may eliminate the needs for such growing rods,it is very possible to utilize such rods within the present invention.In addition, the present invention provides a novel approach for doingthis with higher strength materials than stainless steel.

As materials become higher strength, they often become more notchsensitive or subject to crack propagation from a stress riser. Instainless steel, which is less sensitive to this, a collet can be usedthat grabs features on the rod, such as indentations. As the bodymembers 12 are advanced on the rod 16, the collet grabs anotherindentation. Ideally, with higher strength materials, it is notdesirable to create indentations, but rather utilize smooth rods andstill be able to index the rod in the direction of growth. Thus, thepresent invention provides means for grabbing the rod securely only inone direction while allowing the device to release the rod during theexpansion process and relock after the expansion is completed.

In the preferred embodiment shown in FIGS. 56 and 57, a tapered collet176 and a housing 178 is utilized. The collet 176 compresses securelyagainst the rod 16 when the rod 16 is seated in the collet and thecollet taper engages the taper in the housing 178. A gap towards thelarge end of the taper between the end of the collet 176 and the insideedge of the housing 178 allows the collet 176 to slide into this gapwhen forced to do so, thus freeing the tapers. The rod 16 is thenrelatively free (there is still friction which can be set at the time ofmanufacturing at different levels depending on what is ideal for thegiven surgical situation) to move in the direction shown by arrows 180in FIG. 56. Backwards motion relocks the collet tapers thereby lockingthe assembly. An advantage to this is that very little motion isrequired to unlock and relock the tapers. The ideal taper is what istermed a self-releasing taper or greater than 3°, as anything less wouldbe very hard to disengage.

In view of the above, the present invention provides a uniform loadingsystem. Normal fixation in a single level screw fusion constructsinvolves using at least two rods, one on either side of the spine, andtwo screws per rod. As the screws are fixed rigidly to the rod and thepedicle, there is not adjustment if one screw incurs a higher stressthan another. Curvature of the rods, anatomical alignment, variation ofscrew depth from side to side, and the addition of other components,such as cross links, all contribute to variations in stress. The higherthe variation in stress, the more likely the highest stressed screw orcomponent will fail. By allowing screws to load share and distribute thestresses in accordance with the present invention, this issue becomesgreatly reduced and the loads to the assembly and spine are distributedmore evenly.

A further embodiment of the present invention is shown in FIGS. 58 and59 at 10′″″. In this embodiment, the rod member 16″ includes at leasttwo flat portions 182, 184. The rod is contacted by rounded bearingsurfaces that allow for any degree of bend to occur with only onebearing. This is demonstrated in FIG. 59, in cross-section, wherein thecontact points 186 of the bearing member 188 allow for curvature of therod member 16″ therebetween. Secondly, the stiffness of the rod 16″ canbe adjusted such that the stiffness in the coronal plane can bedifferent than the sagital plane. For example, after derotation, it maybe beneficial to have the stiffness of the rod 16″ in the coronal planebut less stiff than the sagital plane. This would keep the spinestraighter in the medial lateral direction but allow greater flexionanterior/posterior. In other words, selective flexion of the rod andthereby the system can be achieved in a desired plane while rigidity canbe achieved in a different plane. Third, the height of the rod can bereduced to allow for a smaller height of the implant.

In operation, at least three screws at three different points arerequired to reduce a curve. The middle screw is connected to the up andlower screw by rod segments. Adjustment is made by rotating the rodsegments, thereby correcting the abnormal curvature and straighteningthe spine. Derotation would result in straightening of the spine.Sliding of the body members along the rods would allow for growth of thespine. The various locking means above would allow for rotation of therods relative to the body members. It is also possible to lock the rodsin a fixed position once growth is complete via the opening in the body.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology, which has been used is intended tobe in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventioncan be practiced otherwise than as specifically described.

1. A polyaxial screw assembly comprising internal load dampening meansfor sharing and dampening loads between at least one screw member and atleast one rod member interconnected by said assembly; a body membercontaining said load dampening means and slidable rod retaining meansfor retaining a rod member therein while allowing sliding movement ofsaid body member relative to said rod; and screw seat means for seatinga screw head therein, said load dampening means including at least aportion of said screw head seat.
 2. The assembly as set forth in claim1, wherein said load dampening means includes a load dampening membermade of resilient load dampening material seated in said screw headseat.
 3. The assembly as set forth in claim 2, wherein said loaddampening member is a ring.
 4. The assembly as set forth in claim 3,wherein said screw head seat means includes ring retainer means forretaining said ring therein, said ring defining at least one wall ofsaid screw head seat means and providing a biasing surface whereby saidring biases to absorb forces between said screw head and said bodymember.
 5. The assembly as set forth in claim 1, wherein said loaddampening means defines at least a portion of a wall of said screw headseat.
 6. A polyaxial screw assembly comprising internal load dampeningmeans for sharing and dampening loads between at least one screw memberand at least one rod member interconnected by said assembly, and screwseat means for seating a screw head therein, said load dampening meansincluding at least a portion of said screw head seat.
 7. The assembly asset forth in claim 6, wherein said load dampening means includes a loaddampening member made of resilient load dampening material seated insaid screw head seat.
 8. The assembly as set forth in claim 7, whereinsaid load dampening member is a ring.
 9. The assembly as set forth inclaim 8, wherein said screw head seat means includes ring retainer meansfor retaining said ring therein, said ring defining at least one wall ofsaid screw head seat means and providing a biasing surface whereby saidring biases to absorb forces between said screw head and said bodymember.
 10. The assembly as set forth in claim 7, wherein said loaddampening member is a cup.
 11. The assembly as set forth in claim 7,wherein said dampening member is a lining entirely covering a surface ofsaid screw head seat.
 12. The assembly as set forth in claim 7, whereinsaid load dampening means defines at least a portion of a wall of saidscrew head seat.
 13. The assembly as set forth in claim 6, wherein saidload dampening means is a flexible portion of said screw head seat. 14.A polyaxial screw assembly comprising: a body member for interconnectinga screw member to at least one rod member, said body member includingslidable rod retaining means for retaining a rod member therein whileallowing sliding movement of said body member relative to said rod andat least one port having a sleeve member disposed therein having a firstcondition allowing rotation thereof relative to said port whileretaining a portion of a rod member therein and a second conditionlocking the rod member from rotation relative to said port.
 15. Theassembly as set forth in claim 14, wherein said one of said port andscrew member having an opening therein and the other includes adeflectable tab member to be disengaged from said opening for allowingsaid first condition and to be engaged within said opening for allowingsaid second condition.
 16. The assembly as set forth in claim 15,including multiple ports.
 17. The assembly as set forth in claim 16,including rotation means for allowing said slidable rod retaining meansto rotate relative to a screw member locked within said body memberalong an axis defined by a length of said body ports.